In the field of this invention it is known for a multi-mode radio to use two or three different crystals, each chosen to reflect a different mode's operating frequency, which are switched when changing from one operating mode (MA) to another. Such an approach has the advantage that it allows simultaneous multi-mode operation.
However, this approach has the disadvantages that it is not cost effective since it requires a number of different crystals (which are typically very costly, depending on the required accuracy of operating frequency), each of which needs automatic frequency control (AFC), further increasing cost and circuit size.
Also, fast handover between MA's, (for example, GSM to WBCDMA, or WBCDMA to GSM, or GSM to EDGE, or EDGE to WBCDMA) requires that timebase synchronization be maintained between different base stations using different MA's, with ‘deep sleep’ mode (power on and off) capabilities.
International Patent Application No. WO-A1-9821819 (Nokia) describes a frequency generator for use in a mobile communication device. The frequency generator is capable of generating different frequencies for several different modes.
Different frequencies are generated by a common reference frequency oscillator. Luteger division's performed so as to yield a variety of different output frequencies.
There is therefore a need to provide a multi-mode radio communications device using a shared clock source wherein the abovementioned disadvantage(s) may be alleviated.